1. Field of the Invention
This invention relates to an information disk recording and/or reproducing apparatus used as an external storage device of a computer or the like, and more particularly to an optical disk recording and/or reproducing apparatus for recording or reproducing information on an optical disk by using a semiconductor laser.
2. Description of the Prior Art
Optical disk recording and/or reproducing apparatus in which light irradiated from a semiconductor laser is focused to a beam of about 1 m in diameter to record and/or reproduce a data on an optical disk at a high density has been watched with a keen interest recently. Conventional optical disk recording and/or reproducing apparatus is disclosed, for example, in U.S. Pat. No. 4,695,993.
FIG. 34 schematically shows a conventional optical disk recording and/or reproducing apparatus. Reference numeral 1 denotes an optical disk having tracks and divided into sectors for recording and/or reproducing information, 2 denotes an optical head comprising a semiconductor laser or the like, 3 denotes a disk motor for rotating the optical disk 1, 4 denotes data modulating and demodulating circuit for digitally modulating an error correction encoded data or for demodulating a reproducing data reproduced from the optical disk 1, 5 denotes a sector control circuit for controlling the timing to a sector to be recorded or reproduced, 6 denotes a control CPU comprising a microprocessor or the like for controlling the whole of the apparatus shown in FIG. 34, 7 denotes a laser drive head-amp circuit for driving the semiconductor laser and for amplifying a reproducing signal, 8 denotes a focus control circuit for focusing a laser beam on the recording plane of the optical disk 1, and 9 a tracking control circuit for tracking a laser beam to a track of the optical disk 1.
With the above-mentioned arrangement, the operation of a conventional optical disk recording and/or reproducing apparatus will be described below.
First, the case where data is to be recorded on the optical disk 1 will be explained. The control CPU 6 sends the address 10 of a target sector where recording is to take place to the sector control circuit 5. The sector control circuit 5 controls the tracking control circuit 9 to seek the target sector. The address 11 of a detected sector sent from the laser drive head-amp circuit 7 is compared with the address 10 of the target sector, and when detected and target sectors coincide with each other, the data modulating and demodulating circuit 4 is actuated to modulate the data. The laser drive head-amp circuit 7 drives the semiconductor laser of the optical head 2 in response to the modulated data 12 sent from the data modulating and demodulating circuit 4 to form recording pits on the recording plane of the optical disk 1, thus recording data thereon.
The case where data is to be reproduced, after seeking the target sector same manner as in the mentioned above, the sector control circuit 5 actuates the data modulating and demodulating circuit 4 to demodulate reproducing data to be sent to an error detection and correction circuit.
As explained above, a conventional optical disk recording and/or reproducing apparatus effects recording or reproducing of data by assigning the address of a target sector using the control CPU 6.
Recently, information processing systems such as, for example, the engineering work station (EWS) and personal computer have vastly progressed contributing largely rapid improvement in information processing capabilities. In addition, in order to extend such capabilities to the extent as possible, there is a growing tendency toward the provision of external storage devices connected with such information processing systems. The data transfer rate, on which the input output speed of data largely depends, constitutes one of the most important considerations associated with the external storage system.
High data transmissibility is required for an optical disk recording and/or reproducing apparatus having high density, large capacity and data reversibility.
In the optical disk recording and/or reproducing apparatus, however, the recording and/or reproducing of data on an optical disk is carried out using a laser beam irradiated from a semiconductor laser or the like. As the result, data transmissibility is limited depending on the output power limit of a semiconductor laser to be used or the recording sensitivity limit of a recording medium. For example, an optical disk recording and/or reproducing apparatus using an optical disk of 5.25 inches in diameter is said to have a rotational speed limited to about 3600 rpm at present. Also, regarding recording density, the status quo is less than otherwise achievable densities due to the wavelength limitation of the semiconductor laser to be used. Therefore, in the current optical disk recording and/or reproducing apparatus, it is to increase the data transmissibility to exceed present levels. As a result, a problem arises of insufficient data transmissibility when a high performance system is desired.